Lock snapping is a frequently used technique for breaking in a locked place. Typically a burglar obtains a device for snapping the outer end of a double cylinder lock and then applies a torque, usually in the vertical direction if not in combination to both vertical and horizontal directions. The weakest point in a double cylinder lock is the hole usually in the middle of the two cylinder halves, said hole drilled right below the plug for securing the cylinder lock to the door. Once the burglar applies torque to the snap device, the cylinder lock breaks apart and the two broken cylinder halves separate from each other. The cylinder half on the outer side of the door remains on the snap device whereas the cylinder part on the inner side is pushed by the burglar to fall towards the inside of the door. The burglar then inserts a new cylinder lock into the hole and easily opens the lock with his own key. An alternative is to force the deadbolts be received in the body of the lock through use of an L-shaped tool.
EP 2 208 839 relates to a high security lock cylinder with a pre-determined breaking line intended for breaking during a lock snapping attempt. Said line is mechanically weakened to be ruptured in response to a breaking force applied by a snapping tool. When the cylinder lock is broken as a result of an attack, the bridge between the two cylinder halves remains intact and malicious removal of the lock cylinder is prevented. The remaining part of the attacked cylinder is still able to receive the key thus allowing the original key holder still able to lock and unlock the cylinder lock.
DE 10 325 731 relates to an alarm trigger for lock cylinders against unauthorized break-in attempts. The cylinder lock has non-conductive means between two electrically conductive means in a casing which only produces trigger contact when broken or deformed. When the lock cylinder is broken at the bridging part in between the two cylinder halves or it is removed from its dedicated location, the conductive means of the assembly instantly get in contact and thus an alarm signal is triggered. Said assembly does still not prevent the unauthorized person from entering the building, nor does it allow the subsequent use of the original key of the authorized person in order to unlock and lock the door even after the lock snapping attack. Hence, it is a must that the cylinder lock shall be replaced by a new cylinder lock after each and every lock snapping attack. A further disadvantage is the fact that the unauthorized person may enter the building after lock snapping attack and then destroy, deactivate or de-energize the alarm arrangement. Additionally, this device requires an uninterrupted power supply and montage of conductive cables and specifically trained montage personnel. More important than all, the functionality of this assembly seriously relies on a metal part which is subject to metal fatigue in time.
DE 3 913 204 relates to a cylinder lock core protection device which has an outer drilling protection shield for detection of an unauthorized attempt. The unauthorized person may still enter the building after a lock snapping attack, and may then deactivate or destroy the alarm arrangement.
DE 83 08 613 relates to a lock with electrical tapping-alarm signaling device, its housing and a bolt member. The assembly comprises a cover for the alarm triggering mechanism, which is naturally bigger than the lock cylinder itself. Thus said assembly requires an off-size montage space in the door body.
WO 2009/093 090 relates to a signaling device for burglary prevention system with electrical body lock sensors placed on the cylinder lock insert joining an alarm system through wires. This assembly requires an uninterrupted power supply and montage of conductive cables and is not suitable for use in existing doors.
DE 4 104 042 relates to a core protector for a cylinder lock, incorporating a blade directed towards cylinder core for cutting a conducting foil in order to trigger an alarm mechanism. Attempted entry drilling forces push the rosette backwards along bars and the blade cuts the foil, thereby triggering an alarm.